It is common in many food processing applications to remove the outer skin of produce. Peeling of produce is performed for appearance, quality, or other purposes, such as to ensure uniform heating during additional processing operations. Where appearance and/or yield of a product is important, efficient peeling is fundamental to retain as much of the flesh of the produce as possible. Methods of peeling developed for commercial processing involve chemically or mechanically removing the skin from the flesh of the produce.
The tomato processing industry has developed a number of methods for peeling tomatoes where the processor desires that the end product remain firm and void of peel. Typical methods include lye peeling and steam peeling. Lye peeling typically involves submersing or spraying the tomato with a hot caustic solution, such as a 10-15% solution of sodium hydroxide (NaOH) or 7-18% solution of potassium hydroxide (KOH) (Concentrations may vary from 2M to 6M or 8% to 25% depending on commodity, cultivars, maturity, and other factors, such as temperatures used). Under these conditions, the peel of the tomato is softened and removed in a single thin layer with the flesh remaining mostly intact. This method normally results in maximum recovery of tomato flesh mass.
Lye peeling suffers from the disadvantage that a caustic material (NaOH or KOH) is used, resulting in operator hazards and the need to treat the effluent before discharge into the environment. A more preferred method currently used in the industry is to use a lye solution to treat the tomato peel, remove the peel and the peeled tomato from the solution, and then neutralize the solution with an acid, yielding salt and water. The neutralizing of the solution prior to disposal eliminates most of the adverse effect on the environment.
Steam peeling is also used commercially to remove the peel from a tomato. In steam peeling, tomatoes are exposed to steam to loosen the skin, which is then removed by mechanical means. Although more environmentally benign than lye peeling, tomato steam peeling does not yield as much flesh during peel removal as lye peeling, as the exposure of the tomato to high temperature steam causes some heating of the flesh of the tomato as well as the peel. Steam peeling frequently results in inferior peels, where some peel remains adhered to the skin, or the flesh is softened underneath, or both.
As existing methods for peeling produce, such as tomatoes and the like, have certain disadvantages, a need exists for a method of peeling produce to achieve optimum peel removal with minimum yield loss with by-products of the peeling process being environmentally compatible.